1. Field of the Invention
The present invention relates to an engine control apparatus and particularly to an engine control apparatus having a function in which a microcomputer controls the injection of a fuel to be supplied to an engine.
2. Description of the Related Art
It is commonly known that an engine control apparatus that is mounted in a vehicle and has a function of controlling fuel injection is provided with a microcomputer that controls fuel injection for an engine, based on input signals from various kinds of sensors for monitoring the operation status of the engine and the driving condition of the vehicle and a monitoring device that monitors the microcomputer and determines whether or not there exists an abnormality in the microcomputer.
In an engine control apparatus of this kind, a monitoring device that determines whether or not there exists an abnormality in a microcomputer has a function of forcibly resetting and restarting the microcomputer when any abnormality in the microcomputer is detected. It is the objective of the foregoing function that, in the case where there occurs an abnormality in a microcomputer that performs principal control items such as fuel injection control and ignition control for an engine, the microcomputer is restored to a normally controlled state so that abnormal control is prevented from being continuously performed. In general, when a microcomputer is reset, the operations of actuators, such as an injector and the like, which are driven by the microcomputer are interrupted; therefore, fuel injection is interrupted during a reset period from a time instant when the microcomputer is reset to a time instant when normal control is restored after a restart of the microcomputer.
Accordingly, in a conventional engine control apparatus, in the case where, due to an abnormality in a microcomputer caused by a transient factor, a microcomputer is reset, fuel injection is interrupted during a reset period; thus, output torque produced by combustion cannot be obtained. As a result, while the engine is idled, the operation of engine is interrupted in some cases even in the case where resetting and restarting restores the microcomputer to its normal condition. In recent years, thanks to enhancement in the performances of a microcomputer, the reset period has been shortened; however, in the case where the interruption of fuel injection caused during the reset period continues to a time instant after which torque enough to keep the engine rotating cannot be obtained, the interruption of the operation of the engine cannot be prevented.
To date, there has been proposed an engine control apparatus in which, in order to prevent such an interruption of an engine, a monitoring device has an added function for driving an injector and an ignition device (e.g., refer to Japanese Patent Application Laid-Open No. 2006-329129). In a conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-329129, not only is there provided an output driver that drives an injector and an ignition device based on an injection command for the injector and an ignition command for the ignition device from a microcomputer, but also a monitoring device, formed of an auxiliary microcomputer, has an added function in which engine-accelerator-pedal position information, air-intake amount information, rotation speed information, and the like are inputted from various kinds of sensors; the ignition command and the injection command are sequentially created based on these information pieces inputted from the sensors and are outputted to the output driver through serial communication; then the injector and the ignition device are driven. The conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-329129 makes it possible that, when an abnormality once occurs in the main microcomputer, the monitoring device can replace the main microcomputer to perform ignition control and fuel injection control even in the case where the main microcomputer is restored to its normal condition after the abnormality disappears.
Moreover, there has been proposed an engine control apparatus that prevents the engine from being interrupted when, during idling of the engine, there frequently occurs resetting that is not intended by the microcomputer (e.g., refer to Japanese Patent Application Laid-Open No. 2007-218202). A conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-218202 is configured in such a way that, in the case where unintended forcible resetting occurs in a microcomputer, a backup RAM stores initialization processing implementing dates/hours and the number of times of resetting instances at a timing of post-resetting initialization processing; based on the stored initialization processing implementing dates/hours, an initialization processing interval between immediately previous forcible resetting and present forcible resetting is calculated; then, in the case where the calculated initialization processing interval is within a predetermined time period that is preliminarily set because, when the engine is being idled and forcible resetting continually occurs, the engine may stop, the idling rotation speed is raised by a predetermined amount for a predetermined time period, in accordance with the calculated initialization processing interval and the stored number of times of resetting instances. As a result, the engine is prevented from being interrupted when, during idling of the engine, there frequently occurs resetting that is not intended by the microcomputer.
In the conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-329129, the monitoring device has an added function for driving an injector and an ignition device; therefore, it is inevitable that the scale and the cost of the engine control apparatus are increased.
Moreover, even in the case of the conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-218202, when the reset period falls within a specific period, the engine cannot be prevented from being interrupted even though, after the reset period, the amount of air is increased so as to raise the idling rotation speed. FIG. 5 is an explanatory chart for the typical fuel injection pattern of a typical 4-cycle and 4-cylinder engine. In FIG. 5, at predetermined timing, a main fuel injection control means in a microcomputer sequentially injects a fuel in the first cylinder #1, the second cylinder #2, the third cylinder #3, and the fourth cylinder #4 (hereinafter, the cylinders are referred to as #1 cylinder, #2 cylinder, #3 cylinder, and #4 cylinder, respectively). FIG. 5 represents a case where resetting is implemented at a time instant T1 because an abnormality in the microcomputer has been detected, and then restarting through the resetting is completed at a time instant T2, whereupon the microcomputer is restored to normal condition. Because a driving signal transmitted from the microcomputer to the injector is interrupted during the reset period TR, the fuel to be injected in #1 cylinder and #3 cylinder during the reset period TR is not injected. Accordingly, even though the microcomputer is restarted through the resetting and restored to normal condition, #1 cylinder and #3 cylinder do not contribute to combustion of fuel because no fuel has been filled into #1 cylinder and #3 cylinder.
In general, it is well known that, in the case where the engine is being idled and no fuel can be filled into a series of cylinders, the engine is more likely to stop. Therefore, even in the case of the conventional engine control apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-218202, when the reset period corresponds to the period TR in FIG. 5, the engine cannot be prevented from being interrupted even though, after the reset period, the amount of air is increased so as to raise the idling rotation speed.